The overall objective of this proposed research is to characterize the bioavailability and pharmacokinetics of selected anticonvulsants in infant patients with neurologic seizure disorders. The anticonvulsants to be studied are primidone, carbamazepine, clonazepam, and valproic acid. The bioavailability of each anticonvulsant from a crushed tablet or capsule content will be compared with that from a suspension formulation. Infants ranging from 3 to 24 months of age, who are receiving one of the anti-convulsants under study, will be recruited. The patients will receive both a powder preparation and a suspension formulation of the anticonvulsant in a randomized crossover fashion. During each chronic treatment period, the drug dosage will be adjusted until a therapeutic plasma dog concentration is reached. A comparison of the steady-state plasma drug concentration to dose ratio between the two preparations will yield a measure of relative bioavailability. The dosage requirement for the selected anticonvulsants in infants over the 3 to 24 months of age will be examined and compared to literature data on older children and adults. The excretion of intact drug and metabolites in urine will also be measured to ascertain whether changes in drug dosage requirement is due to age differences in absorption or elimination of the drug.